Extended surface rotating biological contactor

ABSTRACT

There is disclosed a rotating biological contactor formed of abutting thin wall sheets arrayed along a central hollow square shaft. The contactor takes several forms. In some forms, the sheets are identical vacuum formed sheets joined face-to-face and back-to-back to define a plurality of spaced radial passages open to the perimeter of the contactor and series of concentric passages extending between, and opening into, adjacent radial passages. The identical sheets may be continuous or built up from circular sectors. In other forms, alternate flat sheets and formed sheets are employed to define a similar arrangement of concentric and radial passages. In still another form, trapazoidal formed sections are employed with flat sheets to define a series of parallel, generally concentric passages and with the radial passages being defined by the space between the side edges of the trapazoidal sections.

Attorney g Firm Quarles 82W United States Patent [191 A 1111 3,82 59 Gass et al. Aug. 6, 1974 EXTENDED SURFACE ROTATING [57] ABSTRACT BIOLOGICAL CONTACTOR There is disclosed a rotating biological contactor Inventors: Donald N. Gass, West Allis; David formed of abutting thin W311 Sheets arrayed along a pmsser, Mequon both f w central hollow square shaft. The contactor takes sev'- eral forms. In some forms, the sheets are identical vac- [73] Asslgnee: Alltotml Curpmatmn, M'lwaukeer uum formed sheets joined face-to-face and back-to- Wrs. back to define a plurality of spaced radial passages [22] Fil d; M 10, 1972 open to the perimeter of the contactor and series of concentric passages extending between, and opening [21] Appl N05 252,038 into, adjacent radial passages. The identical sheets may be continuous or built up from circular sectors. In

52 US. Cl. 210/150, 261/92 other forms, alternate flat Sheets and formed Sheets [51 Int. Cl. B0ld 21/00 are employed to define a Similar arrangement of [58] Field of Search 210/17, 150, 151; 261/92 centric and radial passages In Still another form,

trapazoidal formed sections are employed with flat 5 References Cited sheets to define a series of parallel, generally concen- N E tric passages and with the radial passages being de- 3 227 429 il gg T PATENTS 210/ X fined by the space between the side edges of the el'lZl 3,232,865 2/1966 Quinn et al. trapazodal Seams 3,335,081 8/1967 El-Naggar 2l0/l7 X 3,703,96l 11/1972 Feuer 210/151 29 Claims, 16 Drawing Figures Primary Examiner-John Adee PAIENIEnws em 3827, 559

PAIENIEU SHEEI 2 OF 5 Illll PAIENTEB 3.827. 559

SHEET 5 BF 5 EXTENDED SURFACE ROTATING BIOLOGICAL CONTACTOR BACKGROUND OF THE INVENTION This invention relates to the biological purification of waste water, and particularly to improved forms of ro tating biological contactors which are partially immersed in the waste water to be treated and are rotated to expose aerobic bacterial slimes, which will grow on the contactor surfaces, alternately to nutrients in the waste water and oxygen from the atmosphere above the waste water.

One of the known but, until recently, little utilized methods of biologically treating waste water involves the use of contactor members which provide surfaces for the growth of aerobic bacterial slimes. Commonly, the contactors are rotated in a partially submerged position in the waste water so that the alternate exposure of the contactor surfaces to the waste water and to the oxygen in the atmosphere causes the growth of a bacterial film which coats the contactor surfaces. The bacterial slime on such surfaces consists primarily of aerobic bacteria which have the ability to absorb, adsorb, coagulate and oxidize the undesirable organic constituents of the waste water and to change such constituents into unobjectionable forms of matter. The use of rotating contactor surfaces also increases the transfer of oxygen to the waste water in the tank through which the contactors rotate. This promotes the multiplication or synthesis of the aerobic bacteria already present in the mixed waste water and in the bacterial film, as well as increasing the ability of the aerobic bacteria to act upon the waste water and reduce it to unobjectionable forms.

As early as the beginning of this century it was recognized that maximum efficiency could be approached only by providing as large a surface as possible upon which the biological slimes could grow. Thus, in German Pat. specification No. 135,755 to Weigand, patented Oct. 2l, 1902, it was proposed to construct the contactors as rotating wheels consisting of open porous substances, such as thorn brush, to provide a large surface on which the bacteria will settleand grow. More recently, the large surface area has been attempted to be achieved by using closely spaced circular discs arranged along a shaft and generally constructed of a foamed plastic material. There are, however, practical limits to the amount of surface which can be provided by the closely spaced discs. First, the discs must have substantial thickness so as to provide the necessary lateral stability and strength. Secondly, if the discs are spaced too closely together to achieve a large surface area, the growth of bacterial slime will bridge the space between adjacent discs and actually decrease by far the effective surface area. Thirdly, the closer the discs are spaced together the greater will be the volume of waste water displaced by the discs, thereby reducing the retention time of waste water in the tank and diminishing the biological treatment.

It has also been proposed, in German Pat. application P 18 001.1, published June 25, 1970, to form a contactor assembly from several segment-shaped or cubeshaped filter sections arranged side by side on a supporting framework radiating from a shaft, with the filter sections composed of a plurality of stacked plates which form a wasp nest-like structure.

There are also related methods of biological treatment of waste water in which the desirability of providing a large surface area for the growth of the biomass has been recognized. Thus, in modern forms in the art of trickling filters, a packing consisting of alternating plain sheets and vacuum formed corrugated sheets of thin plastic material has been employed (see U.S. Pat. No. 3,403,095, issued Sept. 24, 1968, to Chipperfield et al; and U.S. Pat. No. 3,260,51 l, issued July 12, 1966 to Greer). Also, in the art of purifying bodies of water by oxidizing the organic matter therein, U.S. Pat. No. 3,235,234, issued Feb. 15, 1966, to Beaudoin discloses a submerged assembly formed of a series of spaced sheets having projections formed thereon which abut against adjacent sheets to form a plurality of serpentine paths between the sheets in both a horizontal and vertical direction. The passages accomodate a flow of water and of oxygen provided by mechanical aeration equipment.

While the foregoing demonstrates that it has long been recognized in both the art of rotating biological contactors and in related arts of biological treatment of waste water that large surface area is necessary for the most efiicient growth of the bacterial slimes, the prior art has not achieved an extended surface rotating biological contactor capable at low cost, of achieving optimum operating capabilities. In the contactors of this invention, a large surface area is achieved in a strong, low cost unit which is lightweight and which displaces aminimum volume of waste water in the tank in which it operates so as to permit a greater volume of waste water to be retained in the tank for treatment.

SUMMARY OF THE INVENTION The invention comprises an extended surface rotating biological contactor having an array of thin-walled, generally circular sheets juxtaposed along a central axis of rotation, with a plurality of circumferentially spaced, radially directed discreet passages formed by adjacent sheets and opening to the periphery of the sheets, and

with a series of generally concentric discreet passages formed by adjacent sheets and extending between adjacent pairs of radial passages and open at each end to a radial passage.

The invention may also reside in such a rotating biological contactor in which the sheets have a central opening which mates with a hollow polygonal shaft for transmitting torque to the sheets, or wherein the central opening in the sheets surrounds a hollow polygonal shaft and is joined thereto by rigid plastic foam disposed between adjacent sheets and the shaft to form a continuous rigid core about the shaft.

The objects of the invention include:

a. providing a rotating biological contactor having a large surface area upon which an aerobic biological slime can grow;

b. providing a rotating biological contactor formed of thin material which is joined together to form a strong, self-supporting, lightweight unit;

c. providing a rotating biological contactor built up from thin, formed sheet material which define a plurality of generally concentric passages through which the waste water and oxygen can circulate as the concentric passages alternately pass through the waste water and the atmosphere above the waste water, and which also define a plurality of radial passages through which waste water and oxygen can enter and leave the concentric passages; and

d. providing a rotating biological contactor formed of thin sheet material which occupies a small volume in the treatment tank in which it is operating to thereby permit a long retention time of waste water in the tank.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2, 3, 4 and are views of a first embodiment of a rotating biological contactor in accordance with the invention; with FIG. lbeing a front view in elevation of a pair of contactors mounted in a treatment shafts 26 joumaled in bearings 27 mounted on the top of the side walls of the tank 22 and connected to a suitable drive mechanism for rotating the contactors and 21. The contactors 20 and 21 may be employed in tanks of various configurations and sizes, and the tank 22 forms no part of the present invention. Accordingly, the tank 22 and its inlet and outlet are shown in stylized form only.

Each of the contactors 20 and 21 comprises a plurality of identical circular, thin wall, formed sheets 28. A pair of sheets 28a and 281) are joined face-to-face to form a disc element 29, and the sheets 28a and 28b of each disc element 29 abut against or are joined to the sheets 28b and 28a, respectively, of each adjacent disc element 29. The sheets 28 are so formed that, when joined together to form a disc element 29, they will define a plurality of spaced radial passages 30 emanating tank, FIG. 2 being a side view of one of the contactors 1 of FIG. 1 as viewed in the plane of the line 2-2 of FIG. 1, and with FIGS. 3, 4 and 5 being several sectional views of the rotating biological contactor taken in the planes of the lines identified in FIGS. 1 and 4, respectively.

FIGS. 6 and 7 are views of a second embodiment of a contactor; with FIG. 6 being a front view in elevation of the contactor with parts broken away for purpose of illustration, and with FIG. 7 being a vertical section view taken in the plane of the line 7-7 of FIG. 6.

FIGS. 8, 9 and 10 are views of a third embodiment of a contactor; with FIG. 8 being a front view in elevation of. the contactor with parts broken away for purpose of illustration, with FIG. 9 being a side view taken in the plane of the line 9-9 of FIG. 8, and with FIG. 10 being a vertical section view taken in the plane of the line 10-10 of FIG. 8.

FIGS. 11 and 12 are views of a fourth embodiment of the invention; with FIG. 11 being a front view in elevation of the contactor with parts broken away for purposes of illustration, and with FIG. 12 being a front view in elevation of a flat sheet forming part of the contactor of FIG. 11.

FIG. 13 is a plan view of a continuous strip of formed thin wall sheet material which may be severed along the lines indicated to form trapazoidal sections.

FIG. 14 is a view in section .of the continuous strip of FIG. 13 taken in the plane of the line 14-14 of FIG. 13.

FIGS. 15 and 16 are views of a fifth embodiment of the invention which utilizes the trapazoidal sections illustrated in FIGS. 13 and 14; with FIG. 15 being a view in front elevation of the contactor and with FIG. 16 being a view in section taken in the plane of the line 16-16 of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-5 representing the first embodiment of the invention, a pair of rotating biological contactors 20 and 21 are mounted in a tank 22 having a water inlet 23 and outlet 24. The contactors 20 and 21 are each mounted at their axis of rotation on a hollow square shaft 25 which in turn is mounted on round stub from a central hub and opening to the periphery of the disc element 29. The two sheets 28a and 28b comprising each disc element 29 are also each shaped to define a series of concentric passages 31a, 31b, 310, etc., which are hexagonal in cross section (see FIG. 3) and which extend between adjacent radial passages 30 and are open to the radial passages 30 at each end. 7

To define the respective radial and concentric passages 30 and 31, each sheet 28 is formed with a central hub portion 32 which lies in one end plane of the sheet 28 and which abuts the identical hub portion 32 of the other sheet 28 of each disc element 29. Each sheet 28 is also formed with alternately disposed end wall portions 33a, 33b, 330, etc., which lie alternately in the plane of the central hub portion 32 and in a second, spaced end plane of the sheet 28. The alternate end wall portions 33 are joined by sloping connecting wall portions 34a, 34b, 340, etc., so that each sheet 28 provides one-half of the surfaces necessary to define the concentric passages 31. Each sheet 28 is further formed with walls 35 which lie in a plane midway between the two end planes of the sheet 28, and which are connected by transition surfaces to the end wall portions 33 for the concentric passage 31, so that each sheet 28 provides one-half of the surfaces defining the radial passages 30.

In addition to the radial passages 30 and concentric passages 31 formed internally of each disc element 29, adjacent disc elements 29 likewise define radial passages 36 and concentric passages 37a, 37b, 370, etc., therebetween. Accordingly, the array of disc elements 29 arranged side by side produce in total a honeycomblike pattern of concentric passages 31 and 37, as shown in FIG. 3, and a continuous series of radial passages 30 and 36 extending along the axis of rotation of the contactor, as shown in FIG. 4, with the concentric passages 31 and 37,0pening at each end into the radial passages 30 and 36, as shown in FIG. 5.

In operation, the contactors 20 and 21 are partially submerged within the waste water in the tank 22. As the contactors 20 and 21 are rotated, waste water will enter into the concentric passages 31 and 37 through the radial passages 30 and 36 as the same are immersed in the waste water, and will flow through the concentric passages 31 and 37 and out of the radial passages 30 and 36 as the radial passages emerge from the waste water. In such manner waste water to be treated is brought in contact with the entire submerged inner and outer surfaces of the contactors 20 and 21. Similarly, the entire inner and outer surfaces of the contactors 20 and 21 are exposed to the oxygen in the atmosphere above the waste water as the atmosphere circulates through the radial and concentric passages. An aerobic bacterial film will grow on the surfaces of the contactors fed by the alternate exposure of the surfaces to the nutrients in the waste water and the oxygen in the atmosphere. When the film builds up to a thickness that will no longer support itself it will slough off and be washed out of the contactor passages by the water movement therethrough. The slime which sloughs off of the contactors can be settled to the bottom of the tank 22 where it can be collected and removed, or the slime can be held in suspension in the waste water for settling and removal at subsequent stages of treatment.

In the first embodiment, as well as in the other embodiments to be described, the sheets 28 are formed from thin sheet material which may have a thickness preferably in the range of .02 inch to .03 inch. The sheets 28 are preferably formed into the shape described by standard vacuum forming methods. The material is preferably a plastic which is biologically inert. Suitable materials include polysytrene and polyethylene. The sheets 28 may be joined together to form the disc elements 29, and the disc elements 29 may be joined together to form the array, by solvent welding in the case of a suitable material such as polystyrene or by other forms of welding, such as sonic welding, in the case of polyethylene where solvent welding cannot be used. The large flat abutting surface areas provided by the end walls 33 minimize problems in welding which might be caused by radial misalignment of adjacent sheets.

The contactor assemblies and 21 present a large surface area upon which biological slime can be grown, in comparison with the foam discs heretofore used for rotating biological contactors. For the same diameter assembly and assuming that the thickness of a disc element 29 is the same as the spacing between the flat surfaces of the foam discs of the prior art, the surface area may be nearly double that of the foam discs. At the same time, because of the thin wall construction-utilized, the contactors 20 and 21 will displace much less volume of waste water in the tank with the result that there is a greater volume of waste water retained in the tank at any one time. The increased waste waterretention time which results increases the removal of the undesirable organic material from the waste water. As compared with standard foam discs, the construction of FIGS. 1 through 5 has about l/lOth the volume.

The size of the radial and concentric passages must be large enough that bacterial slime will not build up to such an extent that the passages are blocked. As an indication only of the order of magnitude of the size of the passages, the distance between the two end planes of each sheet 28 may be about 2/3 of an inch.

In FIGS. 1-5, the first embodiment of the invention has been illustrated with contactors 20 and 21 of a small diameter so as to emphasize the arrangement and disposition of the concentric passages 31 and 37. In use, contactors in accordance with the invention would be of larger relative diameter and accordingly would have many more tiers of concentric passages 31 and 37. When large diameter assemblies are desired it may be difficult to physically handle the sheets 28. FIGS. 6 and 7 illustrate an approach to facilitate the handling and assembly of the large diameter contactors.

In the embodiment of FIGS. 6 and 7, each sheet of the contactor 40 is composed of a group of identical, formed circular sectors 41. In the particular embodiment illustrated, a group of three sectors 41 each having an included angle of nearly 120 are employed to define each sheet. Three sectors 41a defining one sheet are then joined face-to-face with three other sectors 41b defining another sheet to form a disc element. The sectors 41 are formed similar to the continuous sheets 28 of the first embodiment so as to define a plurality of radial passages 42 and concentric passages 43 both between joined sectors of each disc element and between abutting the disc elements. That is, each of the sectors 41 is formed to define one-half of each of the concentric passages 43 and one-half of each of the radial passages 42. Many more radial passages are provided in the contactor 40 of FIGS. 6 and 7 as compared with the contactors 20 and 21 of the first embodiment because of the larger diameter utilized so as to insure sufficient openings for the fiow of water and oxygen into and out of the concentric passages.

To increase the strength of the assembly, the edges 44 of the sectors 41a of one group of a disc element are displaced from the edges 44 of the sectors 41b of the other group by a fixed angle so that no sector 41 has its edges 44 aligned with the edges 44 of the sectors of the group to each side of it. The sectors 41 may be mounted upon a square hollow shaft 45 and the inner perimeter 46 of each sector 41 is preferably defined by a series of concentric squares of the same size as the shaft 45 and angularly displaced from each other by the amount of said fixed angle. With such construction, the square shaft 45 may be utilized to align the sectors 41 relative to each other during assembly.

To increase the capacity to transmit torque between the shaft 45 and the assembly of disc elements, the space between the outer surface of the square shaft 45 and the inner perimeters 46 of the sectors 41, and the space between adjacent sectors 41 at the shaft 45 is preferably filled with a rigid plastic foam 47.

In the embodiment of FIGS. 8-10, the rotating biological contactor 50 is formed of alternate thin wall flat sheets 51 and thin wall formed sheets 52, with each pair of flat and formed sheets 51 and 52 defining a disc element 53 and with the assembly of disc elements 53 mounted on a square hollow shaft 54. The flat sheets 51 are continuous, but the formed sheets 52 are provided with spaced radial cutouts 55 extending outwardly from a central hub portion 56 and increasing in width as the distance from the shaft 54 increases.

The formed sheets 52 are provided, similar to the previous embodiments, with alternately disposed end wall portions 57a, 57b, 570, etc., which lie in the two end planes of the formed sheets 52 and which are joined by sloping connecting wall portions 58a, 58b, 580, etc. Concentric passages 59a, 59b, 59c, etc., are thus defined between each formed sheet 52 and flat sheet 51 of each disc element 53, and additional concentric passages 60a, 60b, 60c, etc., are defined between the formed sheet 52 and the flat sheet 51 of adjacent disc elements 53, as shown in FIG. 10. The concentric passages 59 and 60 are each open at their ends at the radial cutouts 55, and the cutouts 55 together with the flat sheets 51 of adjacent disc elements 53 define the radial passages 61.

The embodiment of FIGS. 8-10 has certain advantages over the previous embodiment. First, it is less expensive because only half of the sheets need be vacuum formed. Secondly, to provide about the same cross sectional area of the concentric passages 59and 60 as in the previous embodiment, the distance between the end planes of each formed sheet 52 will be about double that for the formed sheets of the previous embodiments. This will result in the radial passages 61 being larger and will further reduce the possibility of pluggrng.

The radial passages of the previous embodiments could be formed, similar to the radial passages 61, with increasing cross sectional area as the distance from the axis of rotation increases. This has the advantage of providing the capacity at the radial outer points of the radial passages to accept the increased flow which will naturally occur at such points as the contactor 50 emerges from the waste water.

The embodiment of FIGS. 11 and 12 is similar to that of FIGS. 8-10 in that the contactor 70 is built up of alternate flat sheets 71 and formed sheets 72. However,

the formed sheets 72 are continuous and are shaped similar to the sheets 28 of the first embodiment. That is, the formed sheets 72 include wall portions 73 midway between the end planes of the sheets 72 which provide one-half of a plurality of radial passages 74. Then, the flat sheets 71 are each provided with radial cutouts 75 which match the location of the wall portions 73 so that eachradial passage 74 is defined by the wall portions 73, of each adjacent pair of formed sheets 72. This embodiment has the advantage of being easier to form because it is simple to cut out material in the flat sheets 71 than it is to do the same in formed sheets. Also, the wall portions 73 in the formed sheets 72 tend to hold the end walls and connecting walls defining the concentric passages in place during assembly so that they do not flatten out and grow in diameter.

In the embodiment of FIGS. I316, the contactor 80 is built up from disc elements 81 which comprise a flat circular sheet 82 and a group of trapazoidal, formed sections 83 which together define a formed sheet. As

shown in FIGS. 13 and 14, the trapazoidal formed sections 83 can be produced by cutting from a continuous formed strip 84 having a cross sectional shape as shown in FIG. 14, with alternately disposed end walls 85 located in two spaced planes and joined by connecting walls 86. The trapazoidal sections 83 are circumferentially spaced apart on each flat sheet 82 to thereby define radial passages 87 between the ends of the trapazoidal sections 83. Generally concentric passages 88 are defined between the trapazoidal section 83 and the flat sheet 82 to each side thereof.

The fiat sheets 82 are preferably provided with an inner circular opening 89 which is larger than a square hollow shaft 90 on which the assembly is mounted. A rigid plastic foam 91 is placed about the shaft 90 in the space between the shaft 90 and the central openings 89 in the flat sheets 82 and between adjacent flat sheets 82 at the shaft 90, as shown in FIG. 16. In such manner a solid, rigid foam core is formed about the shaft 90.

The embodiment of FIGS. 13-16 has the advantage that the formed sections 83 can be manufactured using plastic extrusion processes rather than the more costly vacuum forming. The passages 88 are parallel to a tangent to the flat sheets 82 and accordingly are not, strictly speaking, concentric passages. However, the parallel passages 88 are intended to be included within the term generally concentric passages as that term is used throughout the specification and claims.

It will be noted in FIG. 16 that the trapazoidal sections 83 at each level are reversed from the adjacent levels. The purpose for such arrangement is to concentrate the surfaces of contact between the formed sections 82 and the flat sheets 82 at as few points as possible. Then, the points at which the formed sections 83 and flat sheets 82 are welded together are reduced because the formed sections 83 on each side of a flat sheet 82 can be joined to the flat sheet in one step. A similar arrangement for the formed sheets 52 of FIGS. 8-10 and the formed sheets 72 of FIGS. 11 and 12 can be used with the same resulting advantages.

The contactor of each embodiment can be made by joining each sheet to each adjacent sheet so as to form a continuous, joined structure along the entire length of the contactor. At the other extreme, individual disc members may be formed and abutted against adjacent disc members. More commonly, however, a stack of sheets comprising several disc members would be joined together and several stacks would be arrayed to form a length of contactor. A continuous, joined length of contactor will have sufficient strength by reason of the constructions heretofore described so that the central shaft is not needed to support the contactor. A continuous, joined length of contactor may also have a sufficient torque transmitting capacity so that only stub shafts need be applied to the ends of the contactor to support the contactor in the tank and to transmit torque from the powersource to the contactor.

From the foregoing it will be seen that, in accordance with this invention, high surface area contactors can be produced from inexpensive materials, at low cost, with lightweight and low volume.

We claim:

1. An extended surface rotating biological contactor, comprising:

an array of thin walled, generally circular sheets juxtaposed along a central axis of rotation;

a plurality of circumferentially spaced, radially directed discrete passages formed by adjacent sheets; said radial passages opening to the periphery of said sheets; and a series of generally concentric discrete passages formed by adjacent sheets and extending between adjacent pairs of radial passages and open at each end to a radial passage.

2. An extended-surface rotating biological contactor in accordance with claim 1 wherein:

said sheets are identical formed sheets joined alternately face-to-face and back-to-back along said axis of rotation. 3. An extended surface rotating biological contactor in accordance with claim 2 wherein:

each sheet is formed with walls defining one half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet,

whereby radial passages are formed between each joined pair of said sheets.

4. An extended surface rotating biological contactor in accordance with claim 2 wherein:

65 said radial passages are uniformly circumferentially spaced about said sheet, and said concentric passages are each formed as an arc of a circle having its center at said axis of rotation.

5. An extended surface rotating biological contactor in accordance with claim 4 wherein:

each of said sheets is formed with a series of alternately disposed end walls lying in two spaced apart planes generally normal to said axis of rotation and with connecting walls joining alternate end walls to each other to thereby define one-half of said concentric passages; and wherein each of said sheets is formed with walls defining one-half of a plurality of said radial passages including walls which lie intermediate the planes of said end walls of said concentric passages. 6. An extended surface rotating biological contactor in accordance with claim 1 wherein:

each of said sheets comprises a group of identical, formed circular sectors which together define a substantially continuous circular disc, with the sectors of the groups being joined alternately face-toface and back-to-back along said axis of rotation, and wherein the sectors of each group are circumferentially displaced from the abutting sectors of the adjacent groups. 7. An extended surface rotating biological contactor in accordance with claim 1 wherein:

alternate ones of said sheets are flat discs and the others are formed sheets, and each of said formed sheets is so shaped as to define said concentric passages with the abutting adjacent flat discs to each side of said formed sheet. 8. An extended surface rotating biological contactor in accordance with claim 7 wherein:

said radial passages are formed by circumferentially spaced, radial cutouts in each formed sheet. 9. An extended surface rotating biological contactor in accordance with claim 7 wherein:

each formed sheet is shaped to define one-half of a plurality of said radial passages; and each flat disc is provided with matching cutouts at said radial passages, whereby each formed sheet defines a radial passage with the formed sheets to each side thereof.

10. An extended surface rotating biological contactor in accordance with claim 1 wherein:

alternate ones of said sheets are flat discs and the others each comprise a series of circumferentially spaced, trapazoidal, formed elements joined to the flat discs on each side thereof.

11. An extended surface rotating biological contactor in accordance with claim 10 wherein:

each trapazoidal element is shaped to form with said flat sheets a series of generally concentric passages which are aligned parallel to a tangent to said flat discs; and

said radial passages are defined by the circumferential space between said trapazoidal elements.

12. An extended surface rotating biological contactor in accordance with claim 1 wherein the cross sectional area of said radial passages increases as the distance from said axis of rotation increases.

13. An extended surface rotating biological contactor, comprising:

an array of double walled disc elements juxtaposed along a central axis of rotation;

said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open at the periphery of said disc elements,

said disc elements each having a series of internal, generally concentric, discrete passages open at each end to a radially directed passage, and adjacent disc elements defining additional series of genend to a radially directed passage. 14. An extended surface rotating biological contactor in accordance with claim 13 wherein:

each of said disc elements is comprised of a pair of identical thin wall, formed sheets joined face-t0- face, and joined back-to-back with the sheets of adjacent disc elements. 15. An extended surface rotating biological contactor in accordance with claim 14 wherein:

each sheet is formed with walls defining one half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet, whereby radial passages are formed between the sheets of each disc member and between the abutting sheets of each adjacent pair of disc elements. 16. An extended surface rotating biological contactor in accordance with claim 14 wherein:

said radial passages are uniformly circumferentially spaced about said sheet, and said concentric passages are each formed as an arc of a circle having its center at said axis of rotation. 17. An extended surface rotating biological contactor in accordance with claim 16 wherein:

each of said sheets is formed with a series of alternately disposed end walls lying in two spaced apart planes generally normal to said axis of rotation and with connecting walls joining alternate end walls to each other to thereby define one-half of said concentric passages; and wherein each of said sheets is also formed with walls defining one-half of a plurality of said radial passages including walls which lie intermediate the planes of said end walls of said concentric passages. 18. An extended surface rotating biological contactor in accordance with claim 13 wherein:

each of said disc elements comprises a pair of groups of identical thin wall, formed sheets with each group comprised of identical circular sectors forming a substantially continuous circular disc, with l the sectors of each group being joined face-to-face with the sectors of the other group of said pair, and being joined back-to-back with the sectors of the adjacent disc element. 19. An extended surface rotating biological contactor in accordance with claim 18 wherein:

the sectors of each group are circumferentially displaced from the sectors of the other group of said disc element and from the abutting sectors of the adjacent disc elements. 20. An extended surface rotating biological contactor in accordance with claim 13 wherein:

each of said disc elements comprises a flat, thin wall sheet and a formed, thin wall sheet joined to said flat sheet and abutting against the flat sheet of the adjacent disc element, with each formed sheet being so shaped as to define said concentric passages with said flat sheet of its disc element and with the flat sheet of the adjacent disc element. 21. An extended surface rotating biological contactor in accordance with claim 20 wherein:

erally concentric, discrete passages open at each w said radial passages are formed by radial cutouts in each formed sheet, said cutouts being equally circumferentially spaced about said formed sheet. 22. An extended surface rotating biological contactor in accordance with claim 20 wherein:

each formed sheet is shaped to define one-half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet;

and each flat sheet is provided with matching cutouts at said radial passages,

whereby each formed sheet defines radial passages with the formed sheets of the disc element to each side thereof.

23. An extended surface rotating biological contactor in accordance with claim 13 wherein:

each of said disc elements comprises a flat, thin wall sheet and a series of circumferentially spaced, trapazoidal, thin wall formed sheets joined to said flat sheet and abutting against the flat sheet of the adjacent disc element.

24. An extended surface rotating biological contactor in accordance with claim 23 wherein:

each trapazoidal sheet is shaped to form a series of generally concentric passages with said flat sheet which passages are aligned parallel to a tangent to said flat sheet; and

said radial passages are defined by the circumferential spacebetween said trapazoidal sheets.

25. An extended surface rotating biological contactor in accordance with claim 13 wherein the cross sectional area of said radial passages increases as the distance from said axis of rotation increases.

26. An extended surface rotating biological contactor, comprising:

a polygonal shaft;

an array of abutting disc elements mounted on said shaft;

said disc elements each having a central opening with mates with said shaft;

said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open to the periphery of said disc elements; and said disc elements each having a series of internal generally concentric, discrete passages open at each end to a radially directed passage, with adjacent disc elements defining additional series of gen erally concentric, discrete passages open at each end to a radially directed passage.

27. An extended surface rotating biological contactor in accordance with claim 26, wherein:

said shaft is square;

each of said disc elements comprises a pair of groups of identical thin wall formed sheets with each group comprised of identical circular sectors forming a substantially continuous circular disc;

the sectors of each group being circumferentially displaced by a fixed angle from the sectors of the other group of said disc element and from the abutting sectors of the adjacent disc element;

and said central opening of each disc element having a perimeter defined by a series of concentric squares of the size of said shaft and displaced from each other by said fixed angle.

28. An extended surface rotating biological contactor in accordance with claim 27, wherein:

a rigid plastic foam is disposed in the space between said shaft and the perimeters of said central openings of said disc elements and in the spaces between disc elements at said shaft to thereby join the disc elements to said shaft.

29. An extended surface rotating biological contactor, comprising:

a hollow polygonal shaft;

an array of disc elements juxtaposed along said shaft and each having a central opening surrounding said shaft and spaced therefrom;

said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open at the periphery of said disc elements;

said disc elements each having a series of internal generally concentric, discrete passages open at each end to a radially directed passage, and adjacent disc elements defining additional series of generally concentric, discrete passages open at each end to a radially directed passage;

and a rigid plastic foam disposed between said disc elements and said shaft and between adjacent disc elements at said shaft to form a continuous rigid core about said shaft.

. 7 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No3, Dated August 6 1974 Invent0r(s) Donald ass et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line; 23, "polysytrene" should read polystyrene v Column 7 line 4, "embodiment" should read embodiments Column 8, line 7, "82", first occurrence, should read 83 Column 11 line 38, "with" should read which Signed 'and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents FORM P0-105O (10-69) USCOMM-DC 60376-P69 U 5 GOVERNMENT PRINTING OFFICE: 869- 9 o 

1. An extended surface rotating biological contactor, comprising: an array of thin walled, generally circular sheets juxtaposed along a central axis of rotation; a plurality of circumferentially spaced, radially directed discrete passages formed by adjacent sheets; said radial passages opening to the periphery of said sheets; and a series of generally concentric discrete passages formed by adjacent sheetS and extending between adjacent pairs of radial passages and open at each end to a radial passage.
 2. An extended surface rotating biological contactor in accordance with claim 1 wherein: said sheets are identical formed sheets joined alternately face-to-face and back-to-back along said axis of rotation.
 3. An extended surface rotating biological contactor in accordance with claim 2 wherein: each sheet is formed with walls defining one half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet, whereby radial passages are formed between each joined pair of said sheets.
 4. An extended surface rotating biological contactor in accordance with claim 2 wherein: said radial passages are uniformly circumferentially spaced about said sheet, and said concentric passages are each formed as an arc of a circle having its center at said axis of rotation.
 5. An extended surface rotating biological contactor in accordance with claim 4 wherein: each of said sheets is formed with a series of alternately disposed end walls lying in two spaced apart planes generally normal to said axis of rotation and with connecting walls joining alternate end walls to each other to thereby define one-half of said concentric passages; and wherein each of said sheets is formed with walls defining one-half of a plurality of said radial passages including walls which lie intermediate the planes of said end walls of said concentric passages.
 6. An extended surface rotating biological contactor in accordance with claim 1 wherein: each of said sheets comprises a group of identical, formed circular sectors which together define a substantially continuous circular disc, with the sectors of the groups being joined alternately face-to-face and back-to-back along said axis of rotation, and wherein the sectors of each group are circumferentially displaced from the abutting sectors of the adjacent groups.
 7. An extended surface rotating biological contactor in accordance with claim 1 wherein: alternate ones of said sheets are flat discs and the others are formed sheets, and each of said formed sheets is so shaped as to define said concentric passages with the abutting adjacent flat discs to each side of said formed sheet.
 8. An extended surface rotating biological contactor in accordance with claim 7 wherein: said radial passages are formed by circumferentially spaced, radial cutouts in each formed sheet.
 9. An extended surface rotating biological contactor in accordance with claim 7 wherein: each formed sheet is shaped to define one-half of a plurality of said radial passages; and each flat disc is provided with matching cutouts at said radial passages, whereby each formed sheet defines a radial passage with the formed sheets to each side thereof.
 10. An extended surface rotating biological contactor in accordance with claim 1 wherein: alternate ones of said sheets are flat discs and the others each comprise a series of circumferentially spaced, trapazoidal, formed elements joined to the flat discs on each side thereof.
 11. An extended surface rotating biological contactor in accordance with claim 10 wherein: each trapazoidal element is shaped to form with said flat sheets a series of generally concentric passages which are aligned parallel to a tangent to said flat discs; and said radial passages are defined by the circumferential space between said trapazoidal elements.
 12. An extended surface rotating biological contactor in accordance with claim 1 wherein the cross sectional area of said radial passages increases as the distance from said axis of rotation increases.
 13. An extended surface rotating biological contactor, comprising: an array of double walled disc elements juxtaposed along a central axis of rotation; said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open at the periphery oF said disc elements, said disc elements each having a series of internal, generally concentric, discrete passages open at each end to a radially directed passage, and adjacent disc elements defining additional series of generally concentric, discrete passages open at each end to a radially directed passage.
 14. An extended surface rotating biological contactor in accordance with claim 13 wherein: each of said disc elements is comprised of a pair of identical thin wall, formed sheets joined face-to-face, and joined back-to-back with the sheets of adjacent disc elements.
 15. An extended surface rotating biological contactor in accordance with claim 14 wherein: each sheet is formed with walls defining one half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet, whereby radial passages are formed between the sheets of each disc member and between the abutting sheets of each adjacent pair of disc elements.
 16. An extended surface rotating biological contactor in accordance with claim 14 wherein: said radial passages are uniformly circumferentially spaced about said sheet, and said concentric passages are each formed as an arc of a circle having its center at said axis of rotation.
 17. An extended surface rotating biological contactor in accordance with claim 16 wherein: each of said sheets is formed with a series of alternately disposed end walls lying in two spaced apart planes generally normal to said axis of rotation and with connecting walls joining alternate end walls to each other to thereby define one-half of said concentric passages; and wherein each of said sheets is also formed with walls defining one-half of a plurality of said radial passages including walls which lie intermediate the planes of said end walls of said concentric passages.
 18. An extended surface rotating biological contactor in accordance with claim 13 wherein: each of said disc elements comprises a pair of groups of identical thin wall, formed sheets with each group comprised of identical circular sectors forming a substantially continuous circular disc, with the sectors of each group being joined face-to-face with the sectors of the other group of said pair, and being joined back-to-back with the sectors of the adjacent disc element.
 19. An extended surface rotating biological contactor in accordance with claim 18 wherein: the sectors of each group are circumferentially displaced from the sectors of the other group of said disc element and from the abutting sectors of the adjacent disc elements.
 20. An extended surface rotating biological contactor in accordance with claim 13 wherein: each of said disc elements comprises a flat, thin wall sheet and a formed, thin wall sheet joined to said flat sheet and abutting against the flat sheet of the adjacent disc element, with each formed sheet being so shaped as to define said concentric passages with said flat sheet of its disc element and with the flat sheet of the adjacent disc element.
 21. An extended surface rotating biological contactor in accordance with claim 20 wherein: said radial passages are formed by radial cutouts in each formed sheet, said cutouts being equally circumferentially spaced about said formed sheet.
 22. An extended surface rotating biological contactor in accordance with claim 20 wherein: each formed sheet is shaped to define one-half of a plurality of said radial passages which are uniformly circumferentially spaced about said sheet; and each flat sheet is provided with matching cutouts at said radial passages, whereby each formed sheet defines radial passages with the formed sheets of the disc element to each side thereof.
 23. An extended surface rotating biological contactor in accordance with claim 13 wherein: each of said disc elements comprises a flat, thin wall sheet and a series of circumferentially spaced, trapazoidal, thin wall formed sheets joined to said flat sheeT and abutting against the flat sheet of the adjacent disc element.
 24. An extended surface rotating biological contactor in accordance with claim 23 wherein: each trapazoidal sheet is shaped to form a series of generally concentric passages with said flat sheet which passages are aligned parallel to a tangent to said flat sheet; and said radial passages are defined by the circumferential space between said trapazoidal sheets.
 25. An extended surface rotating biological contactor in accordance with claim 13 wherein the cross sectional area of said radial passages increases as the distance from said axis of rotation increases.
 26. An extended surface rotating biological contactor, comprising: a polygonal shaft; an array of abutting disc elements mounted on said shaft; said disc elements each having a central opening with mates with said shaft; said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open to the periphery of said disc elements; and said disc elements each having a series of internal generally concentric, discrete passages open at each end to a radially directed passage, with adjacent disc elements defining additional series of generally concentric, discrete passages open at each end to a radially directed passage.
 27. An extended surface rotating biological contactor in accordance with claim 26, wherein: said shaft is square; each of said disc elements comprises a pair of groups of identical thin wall formed sheets with each group comprised of identical circular sectors forming a substantially continuous circular disc; the sectors of each group being circumferentially displaced by a fixed angle from the sectors of the other group of said disc element and from the abutting sectors of the adjacent disc element; and said central opening of each disc element having a perimeter defined by a series of concentric squares of the size of said shaft and displaced from each other by said fixed angle.
 28. An extended surface rotating biological contactor in accordance with claim 27, wherein: a rigid plastic foam is disposed in the space between said shaft and the perimeters of said central openings of said disc elements and in the spaces between disc elements at said shaft to thereby join the disc elements to said shaft.
 29. An extended surface rotating biological contactor, comprising: a hollow polygonal shaft; an array of disc elements juxtaposed along said shaft and each having a central opening surrounding said shaft and spaced therefrom; said array of disc elements having a plurality of spaced, radially directed, discrete passages which are open at the periphery of said disc elements; said disc elements each having a series of internal generally concentric, discrete passages open at each end to a radially directed passage, and adjacent disc elements defining additional series of generally concentric, discrete passages open at each end to a radially directed passage; and a rigid plastic foam disposed between said disc elements and said shaft and between adjacent disc elements at said shaft to form a continuous rigid core about said shaft. 